Bog-standard seniors in Poland typically make 18k-25k PLN per month, which translates to 216k-300k PLN per year. If you're self-employed in software, you will pay roughly 2k of flat fees per month (health insurance, social security etc.), plus a flat 13% tax. So, your net take home pay will be 163k-237 PLN, or 13.5k-19.75k PLN per month. That's 3k-4.43k EUR take home pay per month. My understanding is that it's not that much lower than what you can get in Germany, while real estate and other costs of living in Poland is much cheaper than in Germany (real estate in Germany is probably easily twice the price in Poland).

The main advantage of Western Europe is the lucrative contract market, where you can make much more money than in usual full time employment. A lot of these contracts are non-remote, so you have to live in a big city in Germany, UK, Sweden etc. to get them. However, some are remote friendly and still pay 500-600 eur per day. I personally work these contracts from Poland, pay my 13% flat tax rate, and am the wealthiest person I know in my age group thanks to it. The disadvantage of this strategy is that, if the economy is in recession (like right now), the contracts dry up first.